Prison violence is distinguished from violence in free society, followed by an outline of the reasons that internal controls are relatively weak in prisons. For example, most of the offenders with well-developed consciences have been filtered out by the criminal justice system before reaching prison. Further, the continuous interaction among numerous violence-prone individuals forcibly confined in a harsh environment fosters norms, values, and beliefs that promote the use of violence in certain situations. Seven types of controls to prevent prison violence are described: physical control; antiviolence norms, values, and beliefs; fear of reprisals; legal and administrative sanctions; the profit motive; social acceptance; and housekeeping considerations. Violence goals are identified, and attention focuses on instrumental prison violence, which has the general goal of obtaining power and status for the aggressor. Expressive prison violence, which has no goal other than to relieve tension, is also discussed. The interplay between these two types of violence is analyzed, and prisoner-staff violence and staff-prisoner violence are both considered.